In turbine components for power generation and aircraft body components, an iron-based alloy having high strength has been used. For example, in the turbine components for power generation, a high Cr steel is used in various components.
In a low-pressure final-stage rotor blade for steam turbines which is particularly required to have strength among the turbine components, a 12Cr steel containing approximately 12 weight % of Cr is used as an alloy having all of strength, oxidation resistance and corrosion resistance. In order to improve power generation efficiency, a longer blade length is advantageous. However, due to the limitation of strength, the limit of the blade length of a 12Cr steel is approximately 1 meter.
Also, there are known low alloy-based high tensile steels such as AISI 4340 and 300M. These alloys are low-alloy steels which can have a tensile strength of a 1800 MPa class and an elongation of approximately 10%. However, the amount of Cr which contributes to corrosion resistance and oxidation resistance is as small as approximately 1%. Therefore, the low-alloy steels cannot be used as a rotor blade for steam turbines. In aircraft uses, there is also often used an alloy which has been subjected to a surface treatment such as plating for the purpose of preventing corrosion caused by, for example, a salt content in the atmosphere.
On the other hand, as an alloy having all of strength, corrosion resistance and oxidation resistance, there is known a high strength stainless steel. As a representative alloy of the high strength stainless steel, there is known a martensite-based precipitation strengthening stainless steel such as PH13-8Mo (PATENT LITERATURE 1).
In this martensite-based precipitation strengthening stainless steel, fine precipitates are dispersed and precipitated in a quenched martensite structure. Accordingly, higher strength can be obtained compared to a quenching-tempering type 12Cr steel. Also, in general, there is contained 10% or more of Cr which contributes to corrosion resistance. Therefore, the martensite-based precipitation strengthening stainless steel is excellent in corrosion resistance and oxidation resistance compared to low-alloy steels.